Pulpstone



Nov. 22, 1955 G. N. JEPPSON PULPSTONE 2 Sheets-Sheet l Filid Aug. 4,1953 IN V EN TOR.

gEDR'GE N. JEPPSUN A True/v5 Y Nov. 22, 1955 G. N. JEPPSON 2,724,222

PULPSTONE Filed Aug. 4, 1953 2 Sheets-Sheet 2 INVENTOR. EEURGE N.JEFF'SUN A TTOENEY United States Patent PULPSTONE George N. Jeppson,Brookfield, Mass., assignor to Norton slpmpany, Worcester, Mass., acorporation of Massausetts Application August 4, 1953, Serial No.372,352

6 Claims. 01. 51-206.4)

The invention relates to segmental pulpstones, and more particularly toimproved means for anchoring abrasive segments to a central support.

One object of the invention is to provide a simple and thoroughlypractical pulpstone. Another object is to provide an improved anchoringmeans for abrasive segments. Another object is to increase substantiallythe breaking strength of the union between the abrasive segments and thecentral support. Another object is to eliminate or reduce cracking orspalling of the abrasive segment due to diiferential expansion of thesegments and the central support.

Another object is to provide an anchoring clamp for abrasive segmentswhereby the clamp may be pre-stressed to the segment. Another object isto provide a clamp with a tie bar whereby the clamp may be adjustablyprestressed to the abrasive segment.

Another object is to provide each segment with a V- shaped bottomsurface to increase the contact area between the segment and theconcrete core. Another object is to provide each segment with a V-shapedbottom which serves in combination with the pie-stressed clamp to givegreater resistance to the pulling out of the clamp, particularly as theresult of centrifugal force in normal operation.

Another object is to provide a thin rubber gasket between the clamp andthe abrasive segment to take up unevennesses of both, and in combinationwith the prestressed clamp to avoid any movement between the clamp andsegment as the result of vibration in normal operation.

Other objects will be in part obvious or in part pointed outhereinafter.

In the accompanying drawings in which is shown one of various possibleembodiments of the mechanical features of the invention,

Fig. 1 is an end elevation of a pulpstone constructed in accordance withthis invention, having parts broken away and shown in section to showdetails of construction;

Fig. 2 is an end elevation, on an enlarged scale, of one of the segmentsshowing the clamp for attaching the segment to the central portion ofthe pulpstone;

Fig. 3 is a cross sectional View, taken approximately on the line 33 ofFig. 2, through the segment and the clamping bracket;

Fig. 4 is a fragmentary elevation of a small portion of the pulpstone,showing the segment shapes and the joint material therebetween; and

Fig. 5 is a modification showing a fragmentary elevation of a pulpstone,showing the arrangement of the equilateral hexagon shaped segments.

A pulpstone has been illustrated in Fig. 1 comprising a plurality ofbonded abrasive segments and a central reinforced concrete core 11. Thesegments are arranged in circular rows to form a hollow body of abrasivesegments with an outer surface of revolution.

The abrasive segments 10 may be made of any suitable abrasive, such assilicon carbide or aluminum oxide, bonded by any suitable bond,vitrified bond being preferable. Other bonds such as phenol-formaldehyderesin, rubber, shellac, magnesium oxy-chloride or metal bond may beused. The abrasive segment is molded to shape by the conventional wellknown molding procedure, after which the segment is fired to mature thebond. As illustrated in the drawings, the peripheral portion of thesegment is hexagonal in shape and each segment is provided with aV-shaped bottom surface 12 to increase the contact area between thesegment and the concrete core.

While the segment is in a green state, that is before firing, grooves 15and 16 are cut into the radial side faces 17 and 18. The upper ends ofthe grooves 15 and 16 are provided with pockets 19 and 20 respectivelyto facilitate clamping.

A clamping unit 25 is formed of steel strips which are rectangular incross section. The clamp 25 comprises two opposed clamping brackets 26and 27 having their upper ends bent inwardly at right angles to thebrackets 26 and 27 respectively to form hooks 28 and 29 which engage thepockets 19 and 20 respectively in the segments 10. The lower ends of thebrackets 26 and 27 are provided with inwardly projecting portions 30 and31 the inner ends of which butt against each other. A tie bar 3-2extends between the brackets 26 and 27 and is fastened thereto by a pairof screws 33 and 34. The screws 33 and 34 pass through clearance holesin the brackets 26 and 27 and are screw threaded into the upwardlyextending portions of the tie bar 32.

As illustrated, the clamps 25 are preferably formed in two halves tofacilitate assembly. If desired, however, the clamp may be formed as asingle U-shaped member having inwardly projecting ends or hooks at theupper ends of the U which may be sprung into place after which a tie barmay be used to pre-stress the clamp to the segment. The clamps 25 areformed of relatively heavy steel flat stock which is rectangular incross section, for example 1%" x "in assembling the clamp 25 on each ofthe segments 10, a piece of resilient rubber 35 and 36 is placed betweenthe brackets 26 and 27 and the grooves 15 and 16. The piece of resilientrubber preferably extends into the pockets 19 and 20. The tie bar 32 isthen placed in position and the clamping screws 33 and 34 are tightenedto pro-stress the clamp to the abrasive segment 10. The clamping screws33 and 34 are preferably tightened by means of a torque wrench tobetween 20 to 30 foot pounds on a three-eighths inch 16 pitch screw. Byuse of the thin sheet of resilient rubber gasket between the clamps andthe segment, unevenness in the clamp and the segment is taken up so thatthe pre-stressed clamp and segment are prevented from moving relative toeach other as the result of vibration due to normal operation of thepulpstone.

After the required number of segments have been thus provided withclamps 25, they are assembled into an annulus with sheets of jointmaterial 13 therebetween. This joint material is preferably thatdescribed in the U. S. Patent No. 2,446,513 to Y. H. Nordstrom, datedAugust 3, 1948, to which reference may be had for details of disclosurenot contained herein.

A reinforcing cage comprising a plurality of concentric reinforcingrings 40, 41 and 42 is placed in position. These rings are made of heavysteel rod and are preferably wired together to hold them in positionduring assembly. The cage consists of a plurality of concentric ringsarranged in different planes to reinforce the stone. Each of these setsof rings is spaced from each other and wired to form an integral cagestructure which may be placed on the mold plate at the time the assemblyof the pulpstone segments is started. As shown in Fig. 1, the clampingbracket 25 projects inwardly between the rows of reinforcing rings 40.

After one row of abrasive segments has been assembled with sheets ofjoint material inserted therebetween, layers of joint material areplaced upon the upper faces of the first row of segments after which asecond row of segments is assembled in a similar manner. After thesuccessive rows of abrasive segments have been completely assembled,they are securely clamped together by circumland cement with sand and asuitable amount of trap rock is poured into place between the moldcenter and the annulus of abrasive segments 10. The concrete mixturefills the entire area between the mold center and the abra- 'sivesegments to form a solid central support integral with the abrasiveannulus which is reinforced by the metal rings of the reinforcing cage.The concrete fills the area between each of the clamps 25 and the tiebars 32, and also between the tie bars 32 and the V-shaped bottomsurfaces of the segments securely to anchor each segment to the concretecenter 11.

In the grinding of wood pulp, the wood logs are forced against theperiphery of the pulpstone under a considerable pressure and normallythe surface of the stone is cooled by a coolant fluid. Occasionally thecoolant is cut off for various reasons, mostly accidental, which permitsthe stone (revolving at 240 R. P. M. or 5,000 S. F. P. M. or more) toheat up due to friction of grinding to a sufficient extent in some casesto char the wood being ground. This is done almost instantaneously anddevelops high temperature on the surface of the pulpstone which due tothe low conductivity of the abrasive structure does not penetrate toorapidly and develops stresses because the outer layer expands ahead ofthe inner layers or increments of the segment. When this strain thusdeveloped exceeds the strength of the structure of the segment, spallingand cracking may occur. In former pulpstones, for example a 62" by 54"stone, occasionally some trouble has been experienced by spalling andbreaking as the result of thermal shock developed in grinding. Thesegments in these particular stones were arranged in five rows ofsegments across the face of the pulpstone and segments around theperiphery thereof. The segments were hexagonal in shape but Weresomewhat longer in the dimension crosswise of the stone so that therewas approximately 9 inches of stone per joint circumferentially andapproximately 13 /2 inches per joint across the face of the stone.

Within reason the smaller the size and the more equidimensional theshape of the abrasive segment, the greater the resistance to thermalshock. I have found that with any construction, particularly the onereferred to, the most equidimensional unit that can be geometricallynested together is an equilateral hexagon with the angles of all corners120 as the nearest approach to the ideal possible. In order to eliminateone of the causes of spalling and cracking of the segments, I havereduced the size and shape of the segment to approximate an equilateralhexagon in shape as shown in Fig. 5, so that in a pulpstone 62 by 54" Ihave eight rows of segments across the face of the stone and 20 segmentsaround the stone thereby decreasing the inches of abrasive per jointacross the face of the stone thus increasing the flexibility across theface of the stone so as to make it more resistant to thermal shock so asto eliminate or minimize spalling and cracking of the segments. .Byshaping thesegments 10 as equilateral hexagons, the sheets of jointmaterial 13 therebetween are of uniform shape and size. The amount ofabrasive material per joint is equal all directions at right angles tothe sides of the hexagon, consequently any expansion of the abrasivesegment is uniformly taken up by compression of the joint material 13.

As shown in Fig. 5, a pulpstone has been illustrated which is formed byeight rows of segments superimposed upon each other in an axialdirection. The marginal rows of segments preferably have one side formedas a plane surface so that the side faces of the stone are in trueradial planes.

It will thus be seen that there has been provided by this invention apulpstone in which the various objects hereinabove set forth togetherwith many thoroughly practical advantages are successfully achieved. Asmany possible embodiments might be made of the mechanical features ofthis invention and as the art herein described might be varied invarious parts, all without departing from the scope of the invention, itis to be understood that all matter hereinbefore set forth or shown inthe accompanying drawings is to be interpreted as illustrative and notin a limiting sense.

I claim:

1. A pulpstone in the shape of a body of revolution, the curved surfaceof which is the outer surface of a plurality of bonded abrasivesegments, comprising a plurality of said bonded abrasive segments, areinforced central concrete core, and a U-shaped clamping memberprestressed onto opposite side face of each of said segments, the openends of said clamping members having inwardly projecting hooksengageable with pockets formed in the opposite sides of said segments,the inner ends of said clamping members being embedded in the concretecore to anchor the segments therein.

2. In a pulpstone, an abrasive segment having an outer abrading surface,a V-shaped inner surface, a plurality of faces between said surfaces, atleast two of said faces being opposed substantially radial faces, apocket formed in each of said faces, a groove on each of said facesextending from the pocket to the inner face of the segment, and asubstantially U-shaped clamping unit, a pair of inwardly projectinghooks formed integral with the outer ends of said unit, the hooks andside portions of said unit being arranged to fit in said pockets andgrooves respectively on opposite sides of said segment, and adjustableconnections between the sides of said unit adjacent to the inner surfaceof said segment whereby the unit may be pre-stressed to said segment.

3. In a pulpstone, an abrasive segment having an outer abrading surface,an inner surface, a plurality of faces between said surfaces, at leasttwo of said faces being opposed substantially radial faces, a pocketformed in each of said radial faces, a groove on each of said facesextending from the pocket to the inner face of the segment, and asubstantially U-shaped clamping unit comprising a pair of radiallyarranged brackets, inwardly projecting hooks at the outer end of each ofsaid brackets which are arranged to engage said pockets from theopposite sides of said segment, inwardly projecting arms of the innerends of said brackets, the inner ends of said arms bearing against eachother to form the inner end of said unit, and adjustable connectionsbetween said brackets adjacent to the inner surface of said segment tofacilitate pre-stressing said clamping unit to said segment.

4. In a pulpstone, an abrasive segment, as claimed in claim 3, incombination with the parts and features therein specified in which theadjustable connections include a tie bar extending between said bracketsadjacent to the inner surface of said segment, and adjustableconnections between the ends of said tie bar and said brackets wherebysaid unit may be pie-stressed to said segment.

5.1m a pulpstone, an abrasive segment, as claimed in claim 3, incombination with the parts and features therein specified in which theinner portion of said U-shaped clamping unit is embedded in the concretecore securely to anchor the segment to the core.

6. In a pulpstone, an abrasive segment for an outer abrading surface, aV-shaped inner surface, a plurality of faces between said surfaces, atleast two of said faces being opposed substantially radial faces, apocket formed on each of said faces, a groove on each of said facesextending from the pocket to the inner face of said segment, and asubstantially U-shaped clamping unit, a pair of inwardly projectinghooks formed integral with the outer ends of said unit, the hooks andside portions of said unit being arranged to fit within said pockets andgrooves respectively on opposite sides of said segment, a resilientgasket between said pocket and grooves and said hooks and side portions,and a tie bar adjustably connected between the sides of said unitwhereby said unit may be pre-stressed to said segment.

References Cited in the file of this patent UNITED STATES PATENTS

